The invention relates to a device for guiding a shaft in an oscillating movement about a point situated on the axis of the shaft, this device applying in particular to the rapid vibration of tubes containing biological samples, for the grinding of these samples by means of small glass or ceramic beads that are contained in the tubes with the samples.
An apparatus is disclosed, particularly in document WO 2004/012851 of the applicant, that comprises a tube-holder plate mounted at one end of a shaft guided in an oscillating movement on a fixed support and driven via its other end that is mounted in an eccentric bearing supported by the output shaft of an electric motor.
The guidance device described in this prior document comprises a set of two concentric bearings, one of which is a ball-and-socket bearing and the other a ball bearing, the ball-and-socket bearing being mounted on the shaft and inside the ball bearing while the ball bearing is mounted between the ball-and-socket bearing and the fixed support.
This known guidance device is very effective: the speed of rotation of the electric motor output shaft may lie between approximately 6500 and 8000 revolutions per minute at normal speed (the samples in the tubes then being subjected to accelerations of approximately 600 to 800 g) and its service life is more than several thousands of operating cycles of 45 seconds every two minutes.
In this known device, the ball-and-socket bearing comprises an inner cylindrical race sleeve-fitted onto the shaft supporting the plate and two rings of balls arranged between this race and an outer race with an internal spherical surface in contact with the balls, that are guided and retained in two semicylindrical grooves in the outer surface of the inner race.
A disadvantage of this known device is the limited possible angular range of movement of the shaft and the plate, that is equal, in the ball-and-socket bearings available on the market, to approximately 4 degrees on either side of a mid-position, which limits the travel of the tubes carried by the plate. To increase this travel and hence the acceleration to which the samples contained in the tubes are subjected, it is necessary to increase the distance between the tubes and the axis of the shaft, which increases the effective diameter of the plate and hence its weight and the energy needed to drive it in an oscillating movement.
The object of the present invention is to enhance this known guidance device, in order in particular to increase the allowed angular range of movement of the shaft on either side of a mid-position or to reduce the diameter of the plate.